The goal of vegetable breeding is to combine various desirable traits in a single variety/hybrid. Such desirable traits may include greater yield, resistance to insects or pests, tolerance to heat and drought, desired earliness, better agronomic quality, higher nutritional value, growth rate and bulb properties.
Breeding techniques take advantage of a plant's method of pollination. There are two general methods of pollination: a plant self-pollinates if pollen from one flower is transferred to the same or another flower of the same plant or plant variety. A plant cross-pollinates if pollen comes to it from a flower of a different plant variety.
Plants that have been self-pollinated and selected for type over many generations become homozygous at almost all gene loci and produce a uniform population of true breeding progeny, a homozygous plant. A cross between two such homozygous plants of different varieties produces a uniform population of hybrid plants that are heterozygous for many gene loci. Conversely, a cross of two plants each heterozygous at a number of loci produces a population of hybrid plants that differ genetically and are not uniform. The resulting non-uniformity makes performance unpredictable.
The development of uniform varieties requires the development of homozygous inbred plants, the crossing of these inbred plants, and the evaluation of the crosses. Pedigree breeding and recurrent selection are examples of breeding methods that have been used to develop inbred plants from breeding populations. Those breeding methods combine the genetic backgrounds from two or more plants or various other broad-based sources into breeding pools from which new lines are developed by selfing and selection of desired phenotypes. The new lines are evaluated to determine which of those have commercial potential.
Onions belong to the lily family, Amaryllidaceae, and the genus Allium. Alliums comprise a group of perennial herbs having bulbous, onion-scented underground leaves, commonly known as onion bulbs, including such commonly cultivated crops as garlic, chives, and shallots. It also includes ornamental species grown for their flowers.
Onions are an important vegetable world-wide, ranking second among all vegetables in economic importance with an estimated production of over 80 million tons in 2012 (FAOSTAT). The onion is also one of the oldest cultivated vegetables in history. In general, the bulb is harvested and eaten. The common garden onions belong to the species Allium cepa. Onions are classified in numerous ways, by basic use, flavor, color, shape of the bulb, and day length. Onions come in white, yellow, and red colors. The bulb may be rounded, flattened, or tapering cylindrical.
Commercial onions include “storage onions”, “fresh onions”, “pearl or mini onions”, and “green onions”. “Fresh onions” tend to have a lighter color with a thin skin, a milder, sweeter flavor, and must be eaten fresh as they do not store well. These onions are available in red, yellow, and white colors.
Storage onions are available from harvest, which is at the beginning of August, and are stored and available throughout the winter months up to about March. Storage onions have a darker skin that is thicker than that of a fresh onion. They are also known for intense, pungent flavor, higher percentage of solids and desirable cooking characteristics. These onions are also available in red, yellow and white colors. Not all long day length type (long day type) onions are suitable for storage. A true storage onion is one that can be harvested in late summer or fall, and stored, under proper conditions, until the spring, when the fresh onion crop is again available.
“Spanish onion”, “Spanish onions”, or “Spanish type” are terms applied to various long-day onions, generally yellow, though some white, and generally varieties that are large and globe-shaped. Spanish onion is commonly applied to various long day type onions of the type grown in western states of the United States (California, Idaho, Oregon, Washington, Colorado) with a bulb size averaging 300-700 grams (g) (typically over 3 inches up to 4 inches but also up to 5 inches in diameter for bulbs classified as “colossal”).
Onion varieties initiate bulbing when both the temperature and a minimum number of daylight hours reach certain levels. When onions are first planted, they initially develop their vegetative growth, with no sign of bulb formation until the proper day length for that onion variety triggers the signal to the plant to stop producing above ground vegetative growth and start forming a bulb. Onions are thus sensitive to the hours of daylight and darkness they receive, and for most varieties it is only when the specific combination of daylight and darkness is reached, that the bulb starts to form. Onions are therefore classified by the degree of day length that will initiate bulb formation. Onions are described as short-, intermediate-, and long-day length types. Short day means that bulbing will initiate at 11 to 12 hours of daylight. Intermediate day is used for onions bulbing at 12 to about 14 hours of daylight. Long day onions require about 14 or more hours of daylight for bulb formation to start.
Growers producing onions in more northerly climates plant long-day length onions. Daylight length varies greatly with latitude, and at higher latitudes long-day onions will produce sufficient top growth before the day length triggers bulbing to produce a large bulb. A short-day onion grown in the North (higher latitudes) will bulb too early and produce relatively small bulbs.
Short day onions are preferred for southern areas such as southern Texas, southern California and Mexico. If a long day type onion is planted in such a short day climate, it may never experience enough day length to trigger the bulbing process.
Onions are also classified on flavor, with the common designations of sweet, mild, and pungent. The flavor of the onion is a result of both the type of onion and the growing conditions. For instance, soils containing a high amount of sulfur result in more pungent flavored onions. Sweetness in onions is caused by the sugars glucose, fructose and sucrose. Onions also contain polymers of fructose called fructans. Onion cultivars differ quite markedly in the relative amounts of sucrose, glucose, fructose and fructans which they contain. They also differ in sugars according to length of storage and location in the bulb. Short day cultivars, which are poor storers, tend to have higher levels of sucrose, fructose and glucose, but hardly any of the fructans. In contrast, long day type cultivars and intermediate storage cultivars such as Pukekohe Longkeeper have less sucrose, glucose and fructose and higher amounts of fructans.
Short day varieties do not keep well in storage conditions, and the pungency of short day varieties can climb considerably during storage. Present production in North America and Europe allows harvest of short day onions from mild winter regions from November through April. Long day onions are available fresh in the late summer and as storage onions from September through March, or even year round, have not been available in low pungency varieties (with the exception of U.S. patent application Ser. No. 12/861,740 which is based on patent application Ser. No. 12/020,360). Sweet onions must be imported from the southern hemisphere to fill the gap in sweet onion production (November-February). In the United States, regions like Georgia and Texas produce short day onions from March to June, while low pungency onions available from November to February are short day onions, produced in the southern hemisphere.
The use of a type of onion is depending on a customer's preference for taste, aroma, appearance and color of an onion. There is thus a need for new short day onions with new appearance and color properties.